The electrostatic force on a small sphere of charge $0.4\mu C$ due to another small sphere of charg

Question

The electrostatic force on a small sphere of charge $0.4\mu C$  due to another small sphere of charge $0.8\mu C$ in air is $0.2	ext{ N}$.  What is the force on the second sphere due to the first?

Professor PC Thomas Classes · Answer

By Newton's Third Law, the electrostatic force between two point charges is equal in magnitude and opposite in direction. Thus, the force on the second sphere is also $0.2	ext{ N}$ and it is attractive.